I don't think any particular Demigod is overpowered, but I do think there are some overpowered abilities.
I think Regulus' mines need to be adjusted so that they aren't holy hand grenades of Antioch.
While I've never experienced it, I've seen evidence that Unclean Beast could use some adjustments as well.
Sedna and QoT seem fine. Sure, they can be unkillable when played properly, but they clearly aren't overpowered. If they'd be a bit more popular. I've played the QoT a lot, and I can say that the shield is awesome early on, but at late game it's really just a support ability for your teammates. Bramble Shield doesn't scale very well, and it just ends up being a small hp buffer near end game. If anything QoT and Sedna need some adjustments.
Torch Bearer and Rook seem to be well balanced.
Oak and Erebus... I'm on the fence about these two; I'm leaning towards them being balanced though.
All in all, I think we'll see minor adjustments here and there, but nothing drastic.